Control apparatus



April 4, 1967 R. w. ARMSTRONG 3,312,1l()

CONTROL APPARATUS Orlginal Filed April 27, 1962 2 Sheets-Sheet 1 FIG. 2

BY LAL ATTORNEY.

April 4, 1967 R. w. ARMSTRONG CONTROL APPARATUS 2 Sheets-Sheet 2(Jrlgnal Filed April 27, 1962 ou u2 nml Ehm monthzv INVENTOR.

ATTORNEY.

3,3 12,1 l@ Patented Apr. 4, 1967 ffice 3,312,110 CNTRUL APPARATUSRobert W. Armstrong, Mound, Minn., assigner to Honeyweii Inc.,Minneapoiis, Minn., a corporation of Delaware Original appiication Apr.2.7, 1962, Ser. No. 191,685, new Patent No. 3,239,140, dated Mar. 8,1966. Divided and this application Apr. 19, 1965, Ser. No. 469,957

1 Claim. (Cl. i3- 407) The present application is a division ofcopending application Ser. No. 191,685, filed Apr. 27, 1962, and nowPatent No. 3,239,140, granted Mar. 8, 1966.

This invention relates to contr-ol apparatus and more particularly toair data computer apparatus utilizing novel static error correctionapparatus to convert signals indicative of indicated static pressure(Psi), to true static pressure (Ps) and provide corrected outputs forthose aircraft components that rely on true static pressure for properindication.

It has long been known in the art that the static pressure received bythe sensing device or Pitot-static tube mounted on an aircraft becomesincorrect by an amount AP which varies as a function of aircraft speedin terms of Mach number M. A relationship may be expressed as:

In the past a number of systems have been proposed to provide acorrected static pressure source but all of these systems have had anumber of disadvantages. Pneumatic systems have been proposed whichemploy a pump or other pressure regulating device controlled inaccordance with the static error pressure AP to adjust the staticpressure in such a manner that the pneumatic output thereof is correctedstatic pressure Ps. These ssytems have had the major disadvantage ofslow response and for the most part are undesirable in the present dayhigh speed aircraft where fast response is critical. Other proposedsystems include electrically rebalanced systems wherein an electricalsignal is generated indicative of corrected static pressure. Suchelectrical systems have had the major disadvantage that the presentstate of the art is incapable of manufacturing accurate enoughcomponents for these systems. `A number of problems result such asundesirable quadrature signals, impedance matching and the like whichalso make such systems undesirable.

The present invention provides an output indicative of corrected staticpressure which is mechanical in nature and as such is not subjected tothe slow response of pneumatic systems nor to the undesirable feature ofelectric systems. Briefly the present invention includes a pressuretransducer having indicated static pressure Ps1 as one input andproviding an output in the form of a shaft `rotation in accordancetherewith. A mechanical static pressure correcting device is providedwhich receives as an input the shaft rotation produced by the transducerdevice and also receives as a second input a shaft rotation which ischaracterized as a function of airspeed in terms of Mach number. Themechanical static error correcting device operates upon these two inputsto provide an output indicative of the static pressure error AP whichoutput is also in the form of a shaft rotation. This AP signal smechanically coupled back -to the transducing apparatus to adjust theapparatus in such a direction that the correction signal AP is combinedwtih the signal indicative of indicated static pressure Psi so that theoutput of the transducer becomes corrected static pressure PS. Theoutput of the transducer which is now corrected static pressure Ps maybe used in the various por-tions of the aircraft instrument wherecorrected static pressure is noted and no further correcton isnecessary. The output of the Static error corrector, as stated, is thecorrection signal AP and this in itself may be used to correct otherinstruments such as the differential pressure transducer.

A more complete understanding of the present invention will be obtainedupon examination of the following specification, claims and drawings inwhich:

FIGURE l is a schematic representation of the basic principle involvedin the static error correction mechamsm;

FIGURE 2 is a partly schematic and partly exploded view of the staticpressure transducer' and static error correcting mechanism employing thepresent invention; yand FIGURE 3 is a block diagram of an air datacomputing system employing static error correction.

Referring now to FIGURE 1, a rotatable arm 10 is shown having alaterally extending flange 12 at one end thereof which contains a pivotaxis 14. The rotatable member 10 has a bearing surface 16 which extendsunder the tiange portion 12 as shown by the dashed line 18.

Also shown in FIGURE 1 is a movable member 20 having a flange portion 22upon which is mounted a bearing member or roller 24. Roller 24 is causedto bear vagainst the bearing surface 16 of member 10 and the pivot axis26 of roller Z4 is such that it is the same distance from the bearingsurface 16 as the pivot axis 14 of member 1?. By this arrangement it isseen that member 20 can be placed so that roller 24 is positioneddirectly under the flange portion 12 of member 10 so that `axis 26 ofroller 2d would coincide with axis 14 of member lil.

Member 2t) is caused by means not shown to move in a vertical directionunder the influence of static pressure and under zero static pressureconditions axis 26 would coincide with axis 14. The verticaldisplacement of axis 26 from coincidence with axis 14 will be controlledaccording to static pressure and in FIGURE 1 this distance has beenshown as the vertical line of a right triangle iden tied with referencenumeral Ps.

Member 10 is caused to rotate as a function of aircraft speed in termsof Mach number. It is known that the static pressure error AP varieswith Mach number in a predetermined fashion and consequently the ratioAID/Ps is also a function of airspeed in terms of Mach number. Bycharacterized means, not shown in FIGURE 1, member 1.0 is caused torotate as a function of are tangent and the amount of rottaion has beenshown in FIGURE 1 as angle 0 which is the angle between the verticalside of the triangle Ps and the line joining axis 14 with axis 26 whichcomprises the hypotenuse of the triangle shown in FIGURE 1.

The amount of horizontal movement of axis 26 from the zero staticpressure condition has been shown in FIG- URE 1 as the distance of thehorizontal portion of lthe triangle identified by reference numeral X.It is clear from FIGURE 1 and the triangle that X :PS tangent 0 andsince, as previously stated, 0 is caused to be a function p are tangentlv X== KP, tangent (are tangent AP P,3 Ps or X: rrr-2.6;) 01- x: KAP

where K is a factor of proportionality determined by the geometry of themechanism.

It is therefore seen that the amount of horizontal displacement of pivotpoint 26 and consequently the hori- Zontal displacement of member 20 isproportional to the static error signal AP and means are provided notshown in FIGURE 1 to measure this horizontal displacement and convert itinto the AP signal used for the remainder of the system.

FIGURE 2 shows a practical embodiment of the present invention includingin the lower portion the static pressure transducer identified byreference numeral and in the upper portion the static error correctionmechanism identified by reference numeral 52.

The static pressure transducer comprises a Z-shaped member which isfixed to the container (not shown) which houses the transducermechanism. Z-shaped member 55 has two oppositely directed flanges 57 and58 at either end thereof which anges have connected thereto a pair ofpressure sensitive devices or bellows 61 and 62 respectively. Bellows 61and 62 are both evacuated in the static pressure transducer 50 while theinterior of the container is supplied with the indicated static pressurePs1 provided from the Pitot-static probe on the aircraft. Thus as theindicated static pressure changes bellows 61 and 62 will each contractor expand. Since bellows 61 and 62 are oppositely directed, they produceforces with changes in indicated static pressure in opposite directions,Bellows 61 and 62 each have a force applying linkage shown in FIGURE 2as bars 66 and 67 respectively. Bars 66 and 67 are connected on oppositesides of a generally O-shaped yoke 70, Yoke 70 is mounted on theZ-shaped member 55 by a quadrilever type spring 72 which is fastened tothe Z-shaped member 55 at the center and which extends in oppositedirections to the yoke 70 where it is fastened as at and 76respectively. This quadrilever type spring 72 provides a spring biasedpivot for 'the yoke 70 and since bellows 61 and 62 apply forces varyingwith Psi to yoke member 70 in opposite directions, changes in Psiproduce a torque on yoke member 70 which turns yoke member 70 withrespect to the Z member 55 by an amount depending upon the stiffness ofthe transducer system spring rate and the amount of change Of PS1.

Yoke member 70 has a lateral extension 86 which is 'in the form of amagnetic armature cooperating with an E-shaped transformer 83 which isconnected to the container housing the transducer 50 by means not shown.It is seen however that rotation of yoke 7i! causes displacernent ofarmature 80 with respect to E transformer 83 whenever the indicatedstatic pressure P51 changes. This displacement of the armature Si) withrespect to the E transformer 83 produces a signal on wires S5, 86 and 87which lead to a motor shown generallyk as 90. Thus any change inindicated static pressure Psi will cause motor to operate in a first orsecond direction depending upon whether PS1 has increased or decreased.Of course, other type pickoif means may be employed in place of Etransformer 83 and if necessary an amplifier may be used between thepickoff and the motor 90.

Motor 90 has an output shown by dashed line 95 which is shown in FIGURE2 terminating at reference numeral A. The dashed line connection isconnected by means not shown in FIGURE 2 to a corresponding referencenumeral A', shown in the upper portion of the drawing, which isconnected by mechanical connection shown as dashed line 96 to a gearsector 98 which forms a portion ofv a torsion tube 10G. As will bedescribed with regard to FIGURE 3, various apparatus may be includedbetween the reference numerals A and A such as gear trains and cams butare not shown in FIGURE 2 for purposes of clarity. Torsion tube has aclamp 162 at the upper end thereof which clamps a torsion bar 104.Torsion bar 194 is shown generally rectangular in cross section andextends down through the torsion tube 100 and down throughl the centerof the quadrilever spring 72 and is clamped to the yoke member 70 at thebottom portion thereof by a clamp 108. It is seen that rotation of motor90 operating through mechanical connections 95 and 96 will causerotation of gear sector 98 and torsion tube 100 to apply a torque to thetorsion bar 104 which in turn transmits this torque to the yoke member70. Rotation of yoke member 70 occasioned by a change in indicatedstatic pressure Ps1 will thus cause movement of armature S0 with respectto a transformer 83 and drive motor 90 in such a direction that therotation of torsion tube 100 and torsion bar 104 applies an oppositelydirected torque to the yoke member 79 to accomplish rebalance of thesystem. That is to say, as soon as yoke member 70 rotates under theinfluence of a change in indicated static pressure Psi an oppositelydirected torque is applied by means of torsion bar 164 to yoke member 70to return it to its original state of equilibrium at which time motor 90stops and the position thereof would be indicative of the new indicatedstatic pressure Ps1.

Also connected to the output of motor 90 is a mechanical connectionshown as dashed line 112 which operates to turn a gear 115 in the staticerror correction mechanism 52. Gear 115 cooperates with a rack 116 whichis part of a member 117 in the static error corrector mechanism 52.Member 117 is provided with guide means such as a trough 120 inwhich apair of rollers 123 and 124 operate. Rollers 123 and 124 are connectedto the frame or casing (not shown) housing the static error correctionmechanism 52. Member 117 also has a lateral extension in the form of afiat plate which extends to the left in FIGURE 2 and which has avertically extending abutment 133 at the remote end thereof. Verticallyextending abutment 133 is also provided with guide means such as atrough 135 in which members such as roller 137 operate. Roller 137 islikewise connected to the frame or casing (not shown) housing the staticerror correction mechanism 52. Rollers 123, 124 and 137 operate to guidemember 117 and the lateral extension 130 in a direction generally intoand out of the plane of the drawing of FIGURE 2. As seen, energizationof motor 90 wil cause rotation of gear 115 which will in turn causemotion of member 117 as guided by rollers 123, 124 and 137.

Member 117 carries a pair of rollers or guide members 141i and 141 andalso carries on the vertically extending abutment 133 a pair of rollersor guide members 144 and 145. Rollers 140, 141, 144 and 145 on member117 cooperate with a generally T-shaped member and operate to guidemember 150 in a direction perpendicular to the motion of member 117.That is to say, T-shaped member 150 is able to move in a directionsubstantially parallel to the plane of the drawing of FIGURE 2.

Member 151) has a lateral extension 153 which in turn carries a guidemember such as a roller 155 thereon. Roller 155 is positioned so as tobear on a surface 160 of a rotatable member 162.

Rotatable member 162 is shown in FIGURE 2 as formed like an open boxthrough which member 150 extends in such a manner that roller 155 cancooperate with the surface 160. Member 162 also has a laterallyextending portion 165 which carries a pivot 166. Pivot 166 is positionedon extension 165 at a distance from surface 160, which extends underextension 165, equal to the distance from the pivot of roller 155 to thesurface 160. This enables roller 155 to occupy a position whereby itspivot is directly under pivot 166. Pivot 166 is connected by bearingmeans (not shown) to the frame or casing housing the static errorcorrection mechanism 52 so that it is free to rotate with respectthereto. Connected to the upper portion of pivot 166 is a follower arm172 which extends to a cam 174 and which has a roller or follower means175 cooperating with the surface of cam 174. Cam 174 in turn has a shaft180 connected thereto which is caused to rotate by means not shown inFIGURE 2 as a function of airspeed in terms of Mach number as indicatedby the larrow and the designation M in FIGURE 2.

In the apparatus thus far described it is seen that rotation of shaftwill cause rotation of cam 174 and will thus cause movement of followerarm 172 which operating through pivot 166 will cause rotatable member162 to rotate. This rotation will be accompanied by movement of theroller 155 to the left or to the right in FIGURE 2 depending upon thedirection of rotation of member 162. Likewise it is seen that rotationof shaft 112 connected to motor 90 will cause rotation of gear 115 andthus cause movement of member 117 generally into or out of the plane ofthe drawing of FIGURE 2. This movement of member 11'7 will beaccompanied by movement of member 156 to the right or to the left sinceroller 155 is caused to bear against surface 160.

As explained with regard to FIGURE l, motion of member 150 to the leftor to the right is a product of the amount of movement of member 117 andthe tangent of the angle through which rotatable member 162 has rotated.As stated, the motion of member 1174 is proportional to static pressureas provided by the motor 9i) and rotation of member 162 is proportionalto a desired function of Mach number. Cam 174 is so characterized thatrotation of member 162 is proportional to the are tangent of the ratioAP/Ps which ratio is known to be a predetermined function of aircraftspeed in terms of Mach number. Thus, motion of member 150 to the leftand to the right is indicative of the correction factor AP since themechanism operates to multiply the ratio AP PS This -motion to the rightor to the left indicative of AP is transmitted from member 15? by meansof a T- shaped extension 19t) at the left end thereof which cooperateswith a guide member or roller 192 connected to a rack 194. Thus motionof member 151B will be ac companied by motion of rack 194 and thismotion is transmitted to a gear 196 which is mounted on a shaft 191i.`It is seen that rotation of shaft 198 is also proportional to the staticerror correction AP. Spring means shown as arrow 200 operate on rack 194to force roller 192 against the T-shaped surface 190 and thus pushmember 150 and roller 155 against the surface 161i of rotatable member162. Spring 200 therefore holds the mechanism in an engaged positionwith the various rollers and surfaces biased towards each other.

As stated shaft 198 rotates in accordance with the static errorcorrection AP and this rotation is imparted to a gear sector 264connected at the lower end thereof.

Gear section 204 cooperates with a gear sector 208 which forms a part ofa member 210. Member 210 has first and second elongated extensions 212and 214 respectively which are attached to a pair of cantilever springmember 216 and 218 as shown by dashed lines 22d and 222. Springs 216 and218 are fastened to the lower portion of yoke member 70 on oppositesides and spaced from clamp 108 by means of a pair of extensions such asshown at 228. It is seen that as gear sector 2114 rotates member 210will rotate which will in turn apply a torque to yoke member 7i) throughsprings 216 and 218. Since the rotation of gear sector 2114 is proportional to that of shaft 198 which in turn is proportional to the staticerror correction quantity AP, the correcting force applied from member210 through springs 216 and 213 to yoke 70 is proportional to the staticerror con rection AP. This correction torque on yoke member 70 causesmovement thereof in a direction which when taken together with thetorque applied from the indicated static pressure Psi provides thenecessary correction and the resultant movement of yoke member 70 isproportional to corrected static pressure PS. Stated differently, themechanism shown in the force transducer 5t)` applies a correcting forceAP which is algebraically summed with the indicated static pressureforce Psi to provide an output Ps which as mentioned is related tocorrected static pressure PS by the equation PS-PS=AP- Thus it is seenthat the pressure transducer Si) has an output propor- XPB aircraft.

6 tional to corrected static pressure Ps which output may be utilized inthe aircraft for those indications where corrected static pressure isnecessary.

Also shown in FIGURE 2 is a member 250 which has a pair of upwardlyextending cylindrical portions 252 and 253. Portions 252 and 253 ofmember 250 when the unit is assembled are attached to the Z-shapedmember SS at holes 250 and 261 respectively as shown by dashed lines 264and 265. Member 250 has a bearing connection with member 210 at theportion between them shown by arrow 27) so that member 210 is free torotate with respect to member 250.

Also shown in FIGURE 2 is a force applying device 27S attached to theyoke member 70 at point 277. Member 275 carries a temperature sensitiveelement 279 which operates to apply a force to the yoke member 70 inaccordance with temperature and thereby provide the transducer 5t) withtemperature compensation.

Also shown in FIGURE 2 is a transducer 300 identified with the letterqc. Transducer 360 is substantially identical in structure to staticpressure transducer S0 herein described and will not be itself describedin detail. The only difference between the qc transducer 300 and thestatic pressure transducer 50 is that the qc transducer produces anoutput proportional to the difference between total pressure PT andstatic pressure PS. This difference is dened as qc and requires that thetransducer have two inputs PT as shown by conduit 303 and Psi as shownby conduit 304. The interior of transducer 300 will be the same as theinterior of the static pressure transducer 5t) herein described exceptthat the bellows 61 and 62 which were described as evacuated in thestatic pressure transducer 5u will have static pressure applied to theirinteriors and total pressure PT in the case will be applied to theirexteriors. Therefore in the qc transducer 3110 motion of the yoke membercorresponding to member 7@ will be in accordance with the differencebetween total pressure PT and static pressure Ps. Transducer 3G() has aninput correcting for the static error AP by means of a shaft 308` whichcorresponds to the shaft 191i for the static pressure transducer 50.Shaft 30S is connected to a gear 31d which is in turn connected to agear 312 mounted on the shaft 198. Therefore as the rack member 194moves in accordance with static error correction AP, gear 312, gear 31dand shaft 368 will rotate accordingly. By a mechanism similar to thatshown in describing the static pressure transducer 50, this correctionfactor AP will be applied to the qc transducer so that its output isindicative of the difference between total pressure PT and correctedstatic pressure Ps.

Referring now to FIGURE 3, which shows in schematic diagram form oneembodiment of an air data computer incorporating the static errorcorrection, a Ps transducer 56', which may be the same as that apparatusshown in FIGURE 2, is shown having an input conduit 400 which providesthe transducer with the pressure Ps1 de rived from the indicated staticpressure source on the A mechanical input shown as dash line 402 isshown connected to transducer 50 to supply the transducer with thecorrection signal AP. Mechanical connection 402 is shown connected by asecond mechanical connection 46S to the static error corrector 52 whichmay be the same as that shown in FIGURE 2. Mechanical connections 402and 405 may comprise the apparatus including roller 192, rack 194, gear196 and shaft 193 of FIGURE 2.

Static pressure transducer 5t) provides an electrical output whenever achange in true static pressure PS causes unbalance of transducer 50.This output is shown in FIGURE 3 as emerging on conductor 407 and beingfed to a summing network 469 which is in turn connected by a conductor411 to an amplifier 412. The output of amplifier 412 drives motor bymeans of a connection 415. Motor 90 in FIGURE 3 is the equivalent ofmotor 94B in FIGURE 2 and the conductor 407, sum- 7 ming network 409,conductor 4H, amplier 412 and connection 4lr5 comprise apparatus placedbetween E transformer 83 and motor 90 which in FIGURE 2 was shown merelyas conductors 85, 86 and 87.

Rate feedback is provided in FIGURE 3 by means of a velocity generator420 connected to motor 90 by a mechanical connection shown as dash line422. The output of velocitygenerator 420 is fed to a resistor 423 by aconductor 424. Resistor 423 includes a movable wiper 425 which isconnected back to the summing network 409 to provide the desired ratefeedback.

The mechanical motion of motor 9) is caused to rebalance the Pstransducer 50 in the following manner. A mechanical connection 427 isplaced between motor 90 and a gear train 429. Gear train 429 has a firstoutput connection 431 leading to a second gear train 432. Gear train 432has mechanical connection 433 leading to a characterized cam shown inFIGURE 3 as a tape cam 435. Cam 435 is so characterized that it convertsmotion indicative of a first condition to a motion indicative of the logof the first condition or vice-versa. Specifically this cam is socharacterized as to convert log of Ps to Ps. Thus if a first portion 437of cam 435 turns as the log of Ps a second portion 438l of cam 435 willturn as PS. Cam 435 has a mechanical connection shown as dash line 440connected to a second mechanical connection shown as dash line 442 to agear train 443 and from there by a mechanical connection shown as dashline 444 to the Ps transducer 50 to accomplish rebalance. Connection 442is also shown providing an input to the static error correctionmechanism 52. The mechanical connections above described between motor90 and Ps transducer 50 including elements 427 through 444 may compriseapparatus between A and A in FIGURE 2. Likewise the connections frommotor 90 to the static error corrector 52 including elements 427 through442 may correspond to the mechanical connection M2 in FIGURE 2,

Because cam 435 is characterized to convert log PS to Ps, motor 9i) iscaused to turn as a function of log PS. Gear trains 429 and 432 operateto reduce the number of turns of motor 90 to a value compatible with thelimited amount of rotation available with cam 435. Since motor 90operates as a function of log Ps, mechanical connections 427, 431 and433 also operate as functions of log Ps. However, mechanical connections440, 442 and 444 operate as a function of Ps itself since they are onthe far side of cam 435. Therefore, as described in connection withFIGURE 2, an input on mechanical connection 442 indicative of PS ispresented t the static error corrector 52 and a rebalance signalindicative of Ps is presented to transducer 50 by mechanicai connection444.

1t has been found that the stability of the above described servo loopchanges as `a function of Static pressure so las to tend to beoverdainped at low pressures. To compenate for lthis change inmechanical gain, a mechainicall connection shown las `dash line 458 isconnected vbetween gear train 432 'and the wiper 425 Aassociated withthe rate feedback ne-twork above described. Mechanical connection 450turns as a function of-log PS as above described and operates toposition wiper 425 so that various amounts of rate feedback dam-ping areprovided depending upon the magnitude of the static pressure. Byproviding more or less rate olf feedback damping signal in accordancewith the magnitude of static pressure, servo loop damping compensationfor the change of stability in the servo loop with change of staticpressure is 'accomplished thus preserving optimum frequency response.

Aiso shown in FIGURE 3 is the qc transducer 300 having a Ps1 input fedthereto by means of conductor 304 and a PT input fed thereto by means ofconduit 303. A mechanical connection from the static error corrector 52is provided for the qc tnansdvucer 300 as t5 shown yby dash lines 460and 405. The mechanical oonnections 405 and 460 may comprise the roller192, nack E94, gears 196, 312 and 3i@ :and the shaft 308 o-f FGURE 2.

An electrical output from the qc transducer is provided on the conductor462 which is shown connected to la summing network 463 and then by aconducto-r 464 to an amplifier 465. Amplifier 465 is connected to iamotor 467 by a connection 463. Rate feedback for this motor is providedby means of a velocity generator 469 connected to motor 467 by aconnection shown as dash line 470. The output of velocity generator 469is presented to a resist-or 472 by a conductor 473. Resistor 472 has awiper 475 connected lback to the summing network 463 to provide therequisite'y nate feedback. The output of motor 467 is shown as a dashline 480 connected to a gear trlain 482.

Rebalance of the qc transducer is provided by a connection shown as dashline 483 from gear train 482 to a second gear train 485. Gear tnain 485is connected to a characterized cam 487 Iby a connection shown as dashline 488. Cam 487 may ybe a tape cam like cam 435 and has a firstportion 489 and a second portion 490. The characterization of cam 487 is`such that as cam 489 rotates as a function of log qc portion 490 willrotate as a function of qc. Cam. 487 is connected to qc transducer 300by mechanical connection sho-wn as dash line 492, a gear train 493 and amechanical connection shown as dash lline 495. Because o-f thecharacterization o-f cam 487, ymotor 467, mechanical connection 480,mechanical connection 483 andnmechianical connection 438 4move asfunctions of log qc whereas mechanical connections 492 and 495 move asfunctions of qc. Con-nection 495 to qc transducer 300 providesrelbalance in much the same fashion as was described with regard to thePs transducer in FIGURE 2. Gear trains 482, 485 and 493 are used forpurposes of converting the amounts of rotation of the shafts to smalleror larger quantities as desired.

As with the PS servo loop, the qc servo floop also changes .grain inaccordance with changes of qc. A similar means of compensating for thischange of gain is shown in FIGURE 3 as a mechanical connection shown asdash line 496 connected :between gear tnain 485 and wiper 475 ofresistor 472. As qc changes, mechanical connection 496 will move wiper475 |to provide more or less rate feedback and to compensate for thechange in gain.

As Ipreviously stated the output of motor is o-perating at the functionof log PS and the output of motor 467 is operating .as Ka function of10g qc. Gear train 429 has a connection shown as dash line 501 connectedto a differential 503. This connection provides an input to thedifferential 503 which is a function of log PS. Gear train 482 has amechanical connection shown as dash line 595 connected to differential503. This provides an input to differential 503 which is a function oflog qc. The output of the differential is the algebnaic :differencebetween the two inputs and this output is shown as dash line 520 inFIGURE 3. The signal on the output connection 510 may be expressed asSince QC:PT-Ps Equation 1 becomes Ps l has long been recognized as afunction of air speed in terms of Mach number and is usually written asR-l where R is defined as PT/PS. The motion of mechanical connnection510 is therefore a function of dog (R-l) which in turn is a function ofMach number. Mechanical connection 510 is shown connected to a geartrain 512 'and then by a mechanical connection shown as dash line 513 toa cam 51S. Cam 515 is shown as a tape cam but unlike cams 435 and 487 ischaracterized to convert the function log (R-1) to -a function of Machnumber M. That is to say, as a first -pontion 517 of cam 515 rotates asa lfunction of log (R-l), a second lportion 519 of cam `5515 moves :as afunction of Mach number M. A mechanical connection shown as `dash line520 connected to cam 515 therefore rotates asa function of Mach numberM. Connected to mechanical connection 5.20 is another mechanicalconnection shown las dash line 52S which is shown 'leading to a cam andfollower arrangement similar to that shown in FIG- URE 2 as cam 174 andfollower arm 172. The purpose of this cam arrangement is to provide anout-put indicative of the quantity xP/Ps which, as `previouslyexplained, is a function of Mach number. This motion is presented to thestatic error corrector 52 by means of -a mechanical connection shown asdash line 527. Mechanical connection 525 may be equivalent to the shaft180 shown in FIGURE 2 While mechanical connection 527 may be equivalentto the ipivot 166 in FIGURE 2. It should be remembered at this pointthat log (R-l) i's in itself a function of Mach number and if desiredconnection 525 could be connected to mechanical connection 510 ratherthan mechanical connection 520 providing cam arrangement 174. 172 werecharacterized so as to converti log (R--1) to a function lof AP/PS.

As shown with regard to FIGURE 2 the :static error correction mechanism52 operating on an input of Ps and an input of AP/Ps produces therequired correction signal AP which is shown in FIGURE 3 as emerging onmechanical connection 405 and is presented to the Ps transducer 50 andthe qc transducer 34N) by mechanical connections 402 and 460respectively to provide the requisite correction for static pressureerror.

In order to produce a number of outputs necessary for aircraft operationthe air data computer 'as shown in FIGURE 3 has 'a variety ofconnections to various Iportions Within the computer each operable toproduce al'desired output. As examples of the kinds of outputsfrequently desired in air data computersFIGURE 3 shows 11 terminalsnumbered 550A through 560. Terminal 550 is shown producing an output ornate of change of log Ps. This output is a known function of rate ofchange of altitude lip. Rate of change of log Ps is easily derived inthe circuit of FIGURE 3 by a connection shown as conduct-or 562connected to the output .conductor 424 of velocity generator 420. Aspreviously stated motor 90 is turning as la function of log Ps andtherefore veloci-ty generator 420 produces an output indicative of rateof change of log PS. Standard characterized means may be employed toconvert the signal d Log P s dT to 75p.

Terminal 551 is shown having an output of log Ps. This output is derivedby a mechanical connection shown as dash line 564 connected to amechanical connection 450 which as [previously mentioned moves as afunction of log Ps. Of course, mechanical connection 564 could beconnected elsewhere in this system and still obtain a signal indicativeof log Ps. For example :an output ifrom gear train 429, mechanicalconnect-ion 431 or mechanical connection 433 could be connected tomechanical connection 564 since each of these connections is moving as afunction of log Ps.

Terminal 552 is shown producing an output Ps This is derived lin FIGURE3 by mechanical connection shown lfd :as ldash line 556 connected tomechanical connectioi 442 which as previously mentioned move-s as yafunction of Ps. As before, mechanical connection 566 could be connectedelsewhere in the circuit and still obtain a Ps output. For exampleconnection 565i? could be connected to connection 444 or lgear train 44?as easily.

Terminal 553 is shown producingan output A log Ps or change of log Psfrom some predetermined value. The change of log Ps output is a knownfunction of chan-ge of altitude hp and may be used las an altitude holdsignal for the aircrafts autopilot. This altitude hold signal is`derived from a connection shown as dash line 568 which is connected toone portion of a clutch S69, the other portion of which 574i) isconnected to gear train 429 by a connection vshown as dash line 571.Clutch 57d may be operated electromagnetically by means of a coil 572.As` previously stated the outputs from gear train 429 operate asfunctions of log Ps and so connection 571 also moves as 'a function oflog Ps. Since log PS is a function of altitude l1, when altitude hold isdesired the coil 572 may be energized by the -pilot thereby engagingclutch members 569 .and 570. From the time of engagement of clutch, asignal is presented to output terminal S53 which -will show change 'oflog Ps from that Wh-ich existed lat the time of engagement. This changeof log PS may be yused thereafter to control the autopilot and hold theaircraft at the ,predetermined desired altitude. Clutch member 569 maybe connected to a -recentering spring not shown to bring clutch member569 back to its initial position when the clutch is again deenergized.

Output terminal 554 is shown producing an output indicative of altitude11p. This is derived from a mechanical connection shown as dash line 575connected to a cam 577. Cam 577 is connected by a mechanical connectionshown as dash line 57S to the mechanical connection 433 which aspreviously stated is moving as Aa function of log Ps. Cam 577 is socharacterized as to convert log Ps to altitude hp.

Output terminal 555 is shown producing an output of indicated air speedVc. This output is obtained by a mechanical connection shown as dashline 580 connected to a cam S82. Cam 582 is connected by a mechanicalconnection shown as dash line 583 to mechanical connection 488. Aspreviously stated mechanical connection 488 is moving as a function oflog qc and hence connection 583 moves as a function of log qc. Cam 582is so characterized as to convert log qc to indicated air speed Vc.

Output terminal 556 is shown producing a Mach num ber output M. This isderived from a mechanical conne'ction shown as dash line 585 connectedto mechanical connection 520 which as ypreviously described moves as afunction of the Mach number.

Output terminal 557 is shown producing an output indicative of change oflog (R1). This in turn is a function of chan-ge in Mach number and maybe used fto produce a sign-al for the autopilot to provide a Mach `holdfunction. The output of terminal 557 is denved Afrom a mechanicalconnection shown 'as dash line 588 which is shown connected to oneportion of a clutch 589, the other portion 590 of -which is connected bya mechanical connection shown as dash line 591 to -mechanical connectionSlo. As previously stated mechanical connection 510 moves `as a`function of log (I2-1) so that mechanical connection 591 similarlymoves. Also as previously stated log (l-1) is a function of Mach number.Clutch members S39 and 59d are engaged by a coil 592 so that `when it isdesired to hold Mach, the pilot may engage members 589 and 59d afterwhich mechanical connection 5&8 moves with mechanical connection 591. Asignal is thus provided indicative of change of Mach number from thevalue existing at the time of engagement. This signal may be sent to theautopilot to provide the desired Mach hold function.

i l As with clutch 569, 570, clutch 589, 59u may be recentered -by meansof a spning not shown so that when the clutch is deenergized member 589will return to its originai position.

Output terminal S53 is shown producing `a signal indicative of qc. Thissignal is obtained from a mechanical connection shown as dash line 593connected to mechanical connection 492. As previously stated connection492 moves as a function of qc so that shaft 593 moves likewise.

Output terminal 559 is shown producing a signal indicative of log qc.This signal is derived from a mechanical connection shown as dash line595 connected to the mechanical connection 4%. As previously statedconnection 496 moves as a function of log qc and hence connection 59Sdoes likewise.

Output 560 is shown producing a signal indicative of d Log (R-l) dT orrate of change of log (R-l). Rate of change of log (R-l) is proportionalto .rate of change of Mach and hence the signal at output 560 may beused to be indicative of Mach rate. This signal is derived from aconductor 600 shown connected to a summing apparatus 602 which may be astandard summing amplifier. Summing apparatus 602 is connected to theoutput of velocity generator 469 by a conductor 604 and is connected tothe output of velocity generator 420 by conductor S62 and a conductor696. A signal from velocity generator 469 is indicative of a rate ofchange of qc whereas the signal from velocity generator 429 isindicative of rate of change of P5. When combined in summing network 602an output is obtained which is indicative of rate of change of 1c/PSwhich as previously defined is a function of rate of change of Mach.

As stated previously with regard to the outputs log Ps and Ps theAconnections leading to the other outputs can be connected elsewherein-the circuit. For example, qc output on 558 could be connected bymechanical connection 593 to connection 495 rather than 492 and the logqc output on termnial 559 could be connected to mechanical connections480, 483 or 483 rather than connection 496. I therefore do not intend tobe limited to the specific connections shown in FIGURE 3 since oneskilled in the art could place the connections to other appropriateplaces to take best advantage of gear train scale factors.

The various shaft outputs 550 through 569 in FIGURE 3 may be connectedto data transmitting devices such as synchros or potentiometers tosupply signals to indicators and autopilot components in a standardstraight forward manner bearing in mind that several of the outputswould necessarily require some characterization before final usage. Forexample with regard to the output at terminal 556 which was stated asvarying with the rate of change of log Ps, when it is desired to providean indication or an autopilot signal indicative of altitude rate thissignal must be characterized to convert `log Ps to 11p. Likewise thealtitude hold and Mach hold signals appearing on terminals 553 and 557are only functions of these conditions and apparatus such ascharacterized potentiometers may be necessary to change A log Ps, toA/zp and A log (R-1) to AM. Such characterization is straight forwardstate i2 of the art procedure and will not be described in detail here.

It is thus seen that apparatus has been provided which produces amechanical output indicative of corrected static pressure Ps and that anair data computer incorporating this apparatus has been providedWhichsupplies a number of useful outputs to be utilized by the aircraft.Also, since static error correction is accomplished at the pressuretransducers, all outputs are compensated for the error in indicatedstatic pressure. It is further seen that the inherent disadvantages inelectrical and pneumatic systems have been overcome by means of thisnovel structure and that the apparatus provided is simple and easilymanufactured and assembled. Furthermore it is noted that the variouspressure transducers identified as the static pressure transducer qchave identically the same form and may be constructed in the same mannerthereby reducing manufacturing costs. Likewise the static errorcorrection mechanism provides an output which may be utilized by -bothof the pressure transducers rather than having a separate corrector foreach transducer. This feature again simplifies the manufacturingprocess. Another advantage is seen in the transducer itself wherein theelements are so arranged around the pivot axis that symmetry isachieved. This is to say the Z-shaped member and the bellows arearranged on opposite sides of the pivot axis so as to minimize anyvibration and acceleration affects that might be produced in the systemwhen it is mounted in an aircraft.

Finally it should be noted that many modifications may be made to thestructure herein described without departing from the spirit of theinvention. For example, it is within the skill of one in the art tomodify the various shapes and connections herein in many obvious ways.

I therefore do not intend to be limited by the specific elementsdescribed in connection with the preferred embodiment but intend only tobe limited by the following claim.

What is claimed is:

Apparatus of the class described comprising in combination:

a fixed member;

a first member pivotally mounted on said fixed member and rotatableabout an axis;

first torque applying means connected directly to said first member andoperable to apply a first torque to said first member about said axis asa function of indicated static pressure Psi;

second torque applying means yresponsive to rotation of said firstmember about said axis for applying a second torque directly to said rstmember about said axis, said second torque being solely in accordancewith static error pressure, AP; and

third torque applying means also responsive to rotation of said firstmember about said axis for applying a third torque directly to saidfirst member about said axis, said third torque being a rebalance torqueand corresponding to true static pressure PS.

References Cited by the Examiner UNITED STATES PATENTS 2,736,199 2/1956Ibott 73-407 X LOUIS R. PRINCE, Primary Examiner.

D. O. WOODILE, Examiner.

